Tape feed mechanism



13 Sheets-Sheet 1 ATTORNEY Oct. 9, 1962 J. A. WEIDENHAMMER ETAL TAPEFEED MECHANISM Original Filed May 28, 1952 mma?,

u lny/ Oct. 9, 1962 .1. A. WEIDENHAMMER ETAL 3,057,568

TAPE FEED MECHANISM Original Filed May 28, 1952 13 Sheets-Sheet 2 FIG. 3

` INVENTORS JAMES A.WEIDENHAMMER WALTER S, BUSLIK ATTORNEY Oct. 9, 1962l J. A. WEIDENHAMMER ErAL 3,057,568

TAPE FEED MECHANISM Original Filed May 28, 1952 l5 Sheets-Sheet 5 FIG. 4H

lNVENTORS JAMES A.WEIDENHAMMER WALTER S. BUSLIK ATTORNEY Oct 9, 1962 J.A. wElDl-:NHAMMER ETAL 3,057,568

TAPE FEED MECHANISM 13 Sheets-Sheet 4 Original Filed May 28, 1952 .ITIIlll l llll INVENTORS JAMES A.WE|DENHAMMER BVALTER S. BUSLIK ATTORNEY J.A. wx-:lDr-:NHAMMER ETAL 3,057,568

Oct. 9, 1962 TAPE FEED MECHANISM 13 Sheets-Sheet 5 Original Filed May28, 1952 FIG. IO

INVENTORS JAMES A WEIDENHAMMER ATTORNEY Oct. 9, A1962 J. A. WEIDENHAMMERET AL 3,057,568

TAPE FEED MECHANISM Original Filed May 28, 1952 15 Sheets-Sheet 6 38 56FIG. l I 3o 28 FIG. I2

i176 \IB4 -WALTER S. BUS

l V ATTORNEY OGL 9, 1962 J. A. WEIDENHAMMER ETAL 3,057,568

TAPE FEED MECHANISM Original Filed May 28, 1952 l5 Sheets-Sheet '7 FIG.I3

INVENTORS JAM A.W IDENHAMMER WAIPER S.EBUSLIK ATTORNEY Oct. 9, 1962 J.A. wElDl-:NHAMMER Erm. 3,057,568

TAPE FEED MECHANISM Original Filed May 28. 1952 13 Sheets-Sheet 8INVENTORS JAMES A WEIDNHAMMER WALTER $.BU LIK Wm/JW ATTORNEY 00t- 9,1962 J. A. wElDl-:NHAMMER ETAL 3,057,568

TAPE FEED MECHANISM Original Filed May 28. 1952 15 Sheets-Sheet 9 FIG.I8

INVENTORS JAMES A.WEIDENHAMMER WALTER S. BUSLIK gym/MM ATTORNEY Oct. 9,1962 J. A. WElDENHAMMl-:R ETAL 3,057,568

TAPE FEED MECHANISM Original Filed May 28, 1952 15 Sheets-Sheet 10INVENTORS JAMES A.WE|DENHAMMER WALTER S. BUSLIK ATTORNEY J. A.wElDl-:NHAMMER ETAL 3,057,568

TAPE FEED MECHANISM 1:5 sheets-sheet 11 ATTORNEY Oct. 9, 1962 OriginalFiled May 28, 1952 06f 9, 1962 J. A. WEIDENHAMMER ETAI. 3,057,568

' TAPE FEED IIEcHANIsIvI Original Filed May 28, 1952 13 Sheets-Sheet 12.

B+ FIG. 27 f-T--RA :1f-RB I I I. .I I ...J

PTI

"' '0V IsoI/ R Io R" THI 'II-I2 30V Q f I MOVING l COIL I PII fbm l I|80 pT3 PT4 I I l I PT2 l -3ovO-- l I TF5 l +I5ov +Iov O-f F I G. 2 8

PTS ,wsu

I BINARY RC' L--J TRIGGER BK I :E :FK

INVENTORS JAMES A.wEIDI:NI-IAMMER WALTER sau LIK BYM/ M /M ATTORNEY Oct.9, 1962 l5 Sheets-Sheet 13 J. A. WEIDENHAMMER ETAL TAPE FEED MECHANISMOriginal Filed May 28. 1952 FIG. 29 ov MRs FRS Z. mjy .f f 1 THCIL" HD@/Ho' svs KR' Luvl Ruv-I W 5 K Luv2 RM RRK '-UV RUV2 RLv-z E: f

l RLv-|/ RLV Rl HD Rol 44a 46a 50a 52a Les Fleo Hf,

Q... ff Ls vPM --J ||5vA.c. `HD

-ofvolmz 22 23 T JAMES 'mm WALTER seus 1K BY/f/ xavm/ ATTORNEY Unite zeClaims. tot. mi2-55.12)

This invention relates to a machine for reeling, unreeling `and feedingtape, this application being a continuation of our prior applicationSerial No. 290,396, tiled May 28, 1952 and now abandoned for Tape FeedMechanism.

More particularly, the invention herein relates to a machine for feedinga record tape through a record reading and/or reproducing head. Theinvention was conceived as an adjunct to an electronic computingmachine, but may be usefully employed in other environments where highspeed tape feeding is a requirement.

With the advent of electronic computing machines, the need for rapiddata input and data recording means has become very acute. Heretoforethe speed at which data could be read from or recorded upon a recordmedium was in part limited by the speed at which existing equipmentcould feed such records through a record sensing or recording station.

The present invention contemplates a record tape feeding mechanismcapable of feeding a record tape through a reading and recording head ata speed of 200 feet per second, with an acceleration and decelerationtime of not more than .005 second, and with the ability to reversedirection of tape feed in ten milliseconds or less.

Production of high speed tape feeding equipment having rapidacceleration, rapid deceleration, and rapid braking rates encounters thedifficulty that record tapes have no great tensile strength and thatmachines designed to handle such tapes must, therefore, impose nosubstantial tension on the tape. It is, therefore, the primary object ofthis invention to provide a record tape feeding mechanism which iscapable of feeding a record tape through a record reading or reproducinghead at high speed without imposing any substantial tension on suchtape.

Itis a further object of the inv-ention to provide a record tape feedingmechanism having a high rate of tape acceleration and deceleration.

It is a further object of the invention to provide a record tape feedingmechanism having tape braking means which is capable of instantaneouslyhalting tape feed.

Withal, it is `an objective of this invention to provide a record tapefeeding mechanism having means for feeding a record tape through arecord reading and/ or reproducing head that imposes a minimum amount oftension on the record tape being fed.

These and other objects and advantages of the invention are attained ina tape feeding mechanism having a pair of tape reels which may beindependently rotated for either reeling or unreeling tape thereon. Itis contemplated that each tape reel be power driven through a clutchmechaanism which is adapted to selectively drive the reel in eitherdirection.

The clutch mechanisms herein are under control of the position of `atape loop depending from each reel and the control system is so designedas to maintain the tape loops substantially constant in length.

'The tape loops provide a tape source upon which a tape feedingmechanism may call `for tape to be fed through a record reading orrecording head in either direction.

The mechanism for feeding the tape through the record reading andrecording head is power driven, Vbut in all States Patent f. .ICQ

respects independent of the power by which the tape reels are rotated.By means of the mechanism briefly described, the tape may be reeled orunreeled and fed through a record reading or reproducing head at highspeed and without substantial tension on the tape.

The details of the mechanism illustrated in the drawings for the purposeof showing an operative embodiment of the invention will become clear asthe description proceeds and in which llike reference numerals indicatelike parts, and wherein;

FIG. 1 is a front elevational view of the tape feeding mechanism withwhich this invention is concerned;

FIG. 2 is a side elevational view of the tape feeding mechanism with theupper portion of the outer casing broken away to show the location ofunderlying mechamsm;

IFIG. 3 is a View on line 3 3 of FIGS. 2 and 4 illustrating the tapedriving mechanism and certain adj-uncts thereto;

FIG. 4 is a plan view of the tape reel drive mechanism comprisingelectromagnetic clutches and brakes;

FIG. 5 is a view on line 5 5 of FIG. 4 showing parts in cross-sectionand other parts in full line;

FIG. 6 is a side elevational view of a vacuum column provided for tapeloop control;

FIG. 7 is a front elevational view of the vacuum column of FIG. 6;

FIG. 8 is a plan View of a vacuum operated switch used in connectionwith the vacuum columns of FIGS. 6 and 7;

FIG. 9 is a cross-sectional view on line 9-9 of FIG. 8;

FIG. 10 illustrates the tape drive mechanism and the means for biasingthe mechanism into tape driving position, the view showing the partsbiased into position for driving the tape in a forward direction;

FIG. 11 is a diagrammatic view of the mechanism shown in FIG. 10 withthe parts thereof biased into position to stop tape movement followingfeed of tape in a forward direction;

FIG. 12 is a diagrammatic view such as that in FIG. 11 and shows themechanism biased into position to effect reverse feed of the tape;

FIG. 13 is a diagramatic view such as those in FIGS. 11 and 12 with theparts biased into position to halt tape feed following reverse feed ofthe tape;

FIG. 14 is a side elevational view of certain tape coil sensingmechanism;

FIG. 15 is a front elevational view of mechanism along line 15-15 ofFIG. 14 showing in particular a pair of tape coil sensing arms andassociated contact operating fingers;

FIG. 16 is a view on line 16-16 of IFIG. 14;

FIG. '17 is a detail view of a lost-motion mounting for the gear elementemployed in the construction of FIGS. 14 through 16;

FIG. 18 is a view correspond-ing in general to FIG. 14, wherein partsare shown in cross-section and showing also the connection -between thetape coil sensing mechanism and a tape reading head mechanism wherebyrelative separation between a tape reading head and its cover iseffective;

FIG. 19 is a sectional view on line 19-19 of FIG. 18 showing theposition of the parts with the tape coil sensing arms in one position;

FIG. 20 is a view similar to that of FIG. 19 but shows the respectiveparts in a different position of adjustment;

FIG. 21 is a view which corresponds in general to FIG. 15 but wherein isshown a modified form of mechanism;

FIG. 2.2 is a cross-sectional view through FIG. 2.1 taken on a line`dis-posed axially in respect to the operating shafts;

FIG. 23 is a view taken from the rear of FIG. 211 to illustrate certainoperating gears and linkages;

FIG. 24 is an elevational view taken from the hack of the deviceillustrating modified mechanism for causing relative separation betweena tape reading head and its cover;

FIG. 25 is a cross-sectional view on line 25-25 of FIG. 24;

FIG. 26 is a transverse cross-sectional view on line 26-26 of FIG. 24;

FIG. 27 is a diagram of the electrical control circuit for controllingtape feed through the tape reading head;

FIG. 28 is a diagram of the electrical control circuit for biasing thetape feed mechanism into forward or reverse feed position;

FIG. 29 is a diagram of the electrical control circuit by which rotationof the tape reels is controlled; and

FIG. 30 is a diagram of the motor control and power supply circuit.

A general understanding of the machine and its function may be attainedby reference to FIGS. 1 and 2 of the drawings. A pair of tape reelsadapted to hold a coil of record tape are intermittently driven toprovide a pair of tape loops upon which the mechanism for feeding thetape through the tape sensing head may call as the tape is to be fed ineither of two directions. A tape reel which we shall designate as a tilereel is mounted on a drive spindle 12. It may be assumed that the reel1G has thereon a coil of tape 14 on which data has been recorded andfrom which the tape is to be fed through a tape reading and recordinghead 16. In its forward feed direction, the tape will pass through thetape reading head 16 and will be coiled on a second reel 18 which may bedesignated herein as a machine reel. The machine reel 18 is mounted on adrive spindle 20.

The file reel drive spindle 12 and the machine reel drive spindle 20 areselectively rotated in either direction by a. pair of motors 22 and 23.The motors 22 and 23 normally impart constant drive to a pair ofelectromagnetic clutch mechanisms mounted on each of the drive spindles12 and 2t). An electromagnetic brake is mounted on each of the drivespindles so that the spindles .12 and 20 may be locked against rotation.The nature of the electromagnetic clutches and the electromagnetic brakewill be developed in greater detail at a later point herein.

Upon selective clutching of the electromagnetic clutch mechanisms indrive relation to the drive spindles 12 and 2), these spindles andconsequently the tape reels attached thereto may be caused to reel orunreel tape from the coil thereon.

Since the mechanism is designed for high speed feed of tape through thetape head 16, it is important that a supply of tape be provided withlittle load or tension thereon, and to this end the driving mechanismfor the reels 10 and 18 provides a pair of tape loops disposed in a pairof tape control columns 24 and 26. Each of the columns 24 and 26 hastherein means responsive to the position of the respective tape loopsfor maintaining a relatively stable position of these loops within thecolumns. The loop sensitive means within the columns 24 and 26 controlthe reel drive mechanism in such manner that the loops, so to speak, areself-compensating. The tape reel drive mechanism for each reel operatesindependently of the other, and both reels are driven independently offeed of tape through the tape head 16.

Tape from the loop supply in the columns 24 and 26 is driven through thetape head 16 by means of a pair of constantly rotating tape drivecapstans. In FIG. 1 a tape drive capstan 28 may be deemed to beconstantly rotated in a clockwise direction, and may consequently bedesignated as the reverse drive capstan. A similar constantly rotatingcapstan 30 may be deemed to be driven in a counterclockwise directionand may, therefore, be designated as the forward drive capstan. Inconnection with the drive capstans 28 and 30, there are provided a pairof tape moving idler pulleys 32 and 34. The pulley 32 is adapted to movea tape trained thereabout into driving contact with the reverse drivecapstan 28, while the tape moving pulley 34 is adapted to move a tapetrained thereabout into driving contact with the forward drive capstan30. As will be pointed out more fully as the description hereofproceeds, the tape moving idler pulleys 32 and 34 are mounted on acommon linkage system which is so designed as to impart the properrelated movement to the pulleys for selectively driving a tape either ina forward or a rearward direction through the tape head 16.

A non-rotary stop capstan is also associated with each of the tapemoving idler pulleys, so that these pulleys may be moved into contactwith their related stop capstans to hold the tape stationary. Thus theidler pulley 32 has associated therewith a stop capstan 36 which weshall designate herein as the forward stop capstan, and the tape movingidler pulley 34 has associated therewith a stop capstan 38 which weshall designate as the reverse stop capstan.

The mechanism for driving the tape reels 10 and 18 may now be referredto in connection with FIGS. 3, 4 and 5 of the drawings. The spindles 12and 2t) are mounted for rotation in a frame member 40. The spindle 12has mounted thereon a le reel brake 42, an electromagnetic reelingclutch 44 and an electromagnetic unreeling clutch 46.

The machine reel spindle 20 has mounted thereon an electromagneticmachine reel brake 43, an electromagnetic nnreeling clutch S0 and anelectromagnetic reeling clutch 52.

The drive rings of the clutch elements 44, 46, 50- and 52 are adaptedfor continuous rotation under the influence of the drive motors 22 and23.

By reference to FIG. 3 of the drawings it will be seen that the drivemotors 22 and 23 are mounted on supporting structures 54 and 56respectively, in such position that the motor shafts `58 and 60respectively extend forwardly into substantially vertical alignment withtheir related magnetic clutch structures.

By reference to FIG. 4 of the drawings it will be seen that the firstpair of clutches 44 and 5G are in substantial, transverse alignment ontheir respective shafts and that the second pair of clutches 46 and 52are also in substantial, transverse alignment on their respectiveshafts. The clutches 44 and 50 are driven in a counterclockwisedirection by the motor 22 through a drive belt 22a while the clutches 46and 52 are driven in a clockwise direction by the motor 23 through adrive belt 23a, thc motor shaft 58 having a normal clockwise rotationand the motor shaft 6d having a normal counterclockwise rotation.

Noting FIG. l of the drawings, it may be seen that the le `reel 10 isdisposed for reeling tape thereon when driven in a counterclockwisedirection, while the machine reel 13 is disposed for tape winding uponclockwise rotation. In light of this arrangement, the clutch 44 operatesas a reeling clutch for the le reel 1t) while the clutch 59 operates :asan unreeling clutch for the machine reel 18. By the same token theclutch 46 operates as an unreeling clutch for the tile reel 10, whilethe clutch 52 operates as a reeling clutch for the machine reel 18.

The le reel brake 42 and the machine reel brake 48 each has the outershell thereof xed to the frame member 40 my means of machine screws 62,thereby providing an anchor for these shells when either brake isenergized to lock its respective shaft against rotation.

FIG. 5 of the drawings illustrates the specific nature of the brake andclutch units. These units are of identical structure, and a descriptionof the clutch 50 will therefore suice as a description of all. Thedriving member 64, including the ring or shell 5t), is mounted on theshaft 20 for free rotation thereon. The driving member includes an endplate 66 in which is mounted a pair of commutator rings 68 which providea current path for an electro magnetic coil 50a mounted within anannular recess in the driven member 64 and held therein by an annularplate 72. The opposite face of the structure has xed thereto a closureplate 74. Suitable hub rings 76 support the driving member for rotationon the shaft A driven member 73 is spaced fromI and disposed between theannular plate 72 and the closure plate 74. The driven member 78 is keyedto the shaft 20 by means of -a suitable keying structure 80.

It will be apparent now that when the driving member 64 and the drivenmember 78 are caused to rotate in unison, drive will be imparted to theshaft 20. Such drive coupling is achieved through the use of iron powderdisposed between the driving member 64 and the driven member 78. Thecircumference of the annular plate 72 is such that its periphery isspaced from the inner wall of the recess formed in the driving member64. rThis in effect forms an annular channel adapted to receive aninturned flange 84 tof the driven member 78. The inturned iiange 84 isso positioned as to provide a substantially equal space on oppositefaces thereof in reference to the oppositely disposed walls of theannular channel. Iron powder ina suificient amount to substantially iillthe remaining space of the channel will serve to freeze the iron powderyand thereby clutch the inturned liange 84 of the driven member 78 tothe driving member 64 of the clutch structure whenever the coil 56a isenergized.

Centrifugal force acting on the iron powder ordinarily maintains thepowder in the channel adjacent the inturned end 84 or" the driven member78. However, in order to avoid possibility of the loss of the powderinto the bearing structure of that assembly, the annular plate 72 isprovided with an annular rib 86 which extends into an annular groove 88on the inner face of the driven member 78. The annular rib 36 isoutwardly slanted to provide a trough for powder that may iind its wayinwardly -along the clutch structure. A similar rib 90 is formed on theouter face of the driven member 78 for preventing passage of powderinwardly along the outer face of the driven member. Any residualparticles of powder will be caught in a lgroove 92 that is formed in theinner face of the driven member near the axial portion thereof.

The commutator rings 68 Iare in contact with a brush 94 carried on theend of a resilient contact strip 96 which is connected into the controlcircuit by means of terminal screws 98 (FIG. 4).

The clutches at the rear end of the spindles 12 and 20 are of the sameconstruction as that described hereinabove, and their mounting on theirrespective shafts is the same except that they are reversed so that theend plate 66 is oppositely disposed to present the commutator rings in amore accessible position. The brake assembles 42 and 48 are alsoconstructed exactly like the clutch assembly just described, and themanner of mounting these on their respective shafts is also the samewith the exception that the end plate 66, and consequently the shell orwhat would correspond in the clutch assembly to the driven member, isheld stationary. It now follows that the energization of the coils inthe several clutch assemblies will result in the corresponding forwardor reverse drive of the respective spindles 12 and 20. By the same tokenthese spindles will be held against rotation whenever the coil in thebrake assembly associated therewith is energized. Since the shells ofthe brakes 42 and 48 are fixed, the leads for energizing theelectromagnetic coils therein may be taken through the end wall of thebrake assemblies. As will be seen at a later point herein, the controlcircuit is such that drive through either of the clutches on a drivespindle will -take place only upon the deenergization of the associatedbrake assembly coil, and that ordinarily the coil in the brake assemblywill be energized to hold its associated spindle against rotation whenthe clutch coils are deenergized.

It has been mentioned heretofore that the position of the tape loops incontrol columns 24 and 26 is utilized to control the rotary movement ofthe tape reels. Herein, by way off example, there has been illustrated avacuum switch control system for achieving this objective. The controlcolumns 24 and 26 are of the same construction, and `the specific naturethereof may best be seen in FIGS. 6 and 7 of the drawings. In theseligures of the drawings is illustrated the control column 26 shown atthe right in FIG. l. However, since the column 24 is of the sameconstruction, ya description of FIGS. 6 and 7 will serve as adescription of both control columns. The column herein illustratedcomprises a pair of side walls 109, a back panel 102, a transparent facepanel 104 and a bottom wall 106, all joined togetheer in airtightcontact.

At the base of the columns 24 and 26 is a header 10S with which thecolumns communicate. The header 1618 is connected with a vacuum pumpadapted to be driven by a suitable motor VPM. The foregoing provides astructure by means of which the control columns 24 and 26 may beevacuated when the upper ends thereof are closed against the atmosphere.

At the upper end of each control column is a lguide plate 112, whosearcuate lower face is slightly spaced from a :corresponding arcuateupper edge of the transparent face panel 104. The lateral extremities ofthe guide plate 112 serve to support the opposite bights of a tape loopwithin the control column and the arcuate slot formed between the lowerarcuate face of the guide block and the upper edge of the face panelconstitutes a guide through which a tape loop may be threaded forinsertion into the control column. The face plate 104 has formed at thebottom thereof a hand opening 114 normally closed by an air-tightclosure 116 held in position by a spring clip 118. This openingconstitutes a cleancut passage.

The side walls of the vacuum columns 24 and 26 are of a widthsubstantially equal to the width of the tape 14. When a tape loop isformed, therefore, in either of the vacuum columns 24 or 26, `theoppositely disposed marginal edges `of the loop will be in substantialcontact with the base plate 102 and the face plate 104 of the respectivevacuum columns. The back of the tape in the tape loop is spaced from theside walls of the vacuum columns through substantially the entire lengthof the loop but Ithe lbight of the loop is in substantial contact withthe side walls. This disposition of the tape loop within the vacuumcolumns 24 and 26 is assured by the tape guide structure. As Ithe tapecomes from the le reel 10, it passes over a guide idler 10a. As the tapeis fed to and from the machine reel 18, it too passes over a guide idler18a. The horizontal distance between the outer periphery of the guideidler 10a and the drive capstan 28 is somewhat less than the spacing ofthe inner faces of the column side walls 100. The same is true of thehorizontal spacing of the guide idler 18a and the drive capstan 30 atthe right of the structure.

The particular horizontal spacing of the guide idlers and theirassociated drive capstans assures that the inner face of the tape is incontact with the oppositely disposed ends of the guide plate 112 at thetop of the vacuum columns 24 and 26. These guide plates, therefore,determine the spacing of the tape bights at the entrance to the columns.Since the distance between the ends of the guide plate 112 is somewhatless than the internal width of the vacuum columns, the back of the tapewill be spaced slightly from the column side walls through the majorportion of the tape loops, the loops, however, widening out at theirlower ends to contact the side walls of the columns, thereby forming anair seal between the lower portion of the tape loop and the columnwalls.

Spaced along the length of each of the control columns 24 and 26- are`two vacuum operated switches, the details of which are sho-wn in FIGS.8 and 9. In FIG. 1 of the drawings the vacuum switch LUV is the leftupper vacuum switch, while the switch LLV is the left lower vacuumswitch. In similar fashion the control column 26 has a right uppervacuum switch RUV and a right lower vacuum switch RLV.

The vacuum switches have a normally closed contact point and a normallyopen contact point. The switches communicate with the interior of theirrespective control columns through an aperture in the back plate 102thereof. By reference to FIG. 9 it will be seen that the switchstructure is encased in a shell 120 which lits tightly against a baseplate 122, the base plate being attached to the back panel 102 of thecontrol column so that an aperture 124 of the back panel registers witha passage 126 in the base 122 of the switch structure. Within a cavityformed between the -base plate 122 of lthe switch structure and anoverlying block 128 is a pressure responsive diaphragm 130` to which acontact operating shaft 132 is attached, this connection between thediaphragm and the shaft 132 being air-tight. 'Adjustably secured to theopposite end of the contact operating shaft 132 is a spring contactlinger 134 having contact points thereon adapted to contactcorresponding points on fixed contact lingers 136 and 140.

In FIG. 9 the spring contact linger 134 has a contact point on the uppersurface thereof which is adapted to engage a Contact point on the lixedcontact nger 136. These contacts are normally closed contacts and aredesignated herein as the RUV-l contacts. On the lower face of the springcontact linger 134 is a second contact point which is adapted to engagea corresponding contact point on the fixed contact linger 140. Thesecontact points are normally open and are designated herein as the RUV-2contact points. ln FIG. 9 the contact points shown therein areassociated with the upper right vacuum switch. A similar structure -isprovided for the right lower vacuum switch RLV, the left upper vacuumswitch LUV and the left lower vacuum switch LLV (FlG. l). ln the circuitdescription in respect to FIG. 29 of the drawings it will be seen thatthe left upper vacuum switch LUV has a pair of points LUV-1 and LUV-2which correspond to the points RUV-l and RUV-Z described in connectionwith FIG. 9. The same is true of the points in vacuum switches LLV andRLV.

Under the foregoing conditions, any time that a switch diaphragm such as13G, for example, is subjected to vacuum within its vacuum column,atmospheric pressure on the opposite side of the diaphragm will causetransfer of the switch points, i.e. the points RUV-l of FIG. 9, forexample, will open, while the points RUV-Z will close.

Electrical connections with the switch blades are made through aconnecting bushing 138 at one end of the base plate 122.

During normal operation of the machine, the tape loops in columns 24 and26 will be disposed between switches RUV-RLV and LUV--LLV of therespective column pairs. Under lthese conditions the switches LUV andRUV are subject to atmospheric pressure only, whereas switches LL andRLV are inliuenced by vacuum in the columns 24 and 26, the tape loopsconstituting a column air seal above the switches LLV and RLV.

The device is designed so that the tape loops in the control columns 24and 26 are maintained between the respective upper and lower vacuumswitches. To this end the vacuum switch LUV is in the control circuit ofthe magnetic coil in the unreeling clutch 46, while the vacuum switchLLV is in the control circuit for .the magnetic coil of the reelingclutch 44. In like manner the vacuum switch RUV is in the controlcircuit of the unreeling clutch 50, while the vacuum switch RLV is inthe control circuit for .the reeling clutch 52.

Should either tape loop drop below its lower vacuum switch, such switchwill lbe subject to atmospheric pressure on both sides of its diaphragm130, causing the contact points thereof lto transfer. Consequently,under such conditions the switch LLV will call into action the 8 lilereel reeling clutch 44 and the switch RLV will call into operation themachine reel reeling clutch 52.

Such tape loops will be taken up by the reeling action of the respectivereels, or either thereof, until the bight of the loop is above the lowercontrol column switch, whereupon `the switch will again transfer itscontact points under inuence of vacuum within the column.

In like fashion the upper vacuum switches LUV and RUV which aresubjected to atmospheric pressure on both sides during normal operationof the machine will transfer their contact points when the bight of thetape loop rises above these switches. Under these conditions the upperswitch will be subject to the vacuum within their respective controlcolumns. The low pressure on the inner side of the diaphragm 136 willthereupon permit atmospheric pressure on the opposite side to transferthe contact points of the upper switch structure. Upon such transfer theswitch LUV will serve to energize the coil in the unreeling clutch 46,and the switch RUV will call into action the unreeling clutch 50 wherebythe lile reel il@ and machine reel 13 respectively, or either one ofthem, will be rotated to unreel tape therefrom and thereby lengthen theloop in the control columns 24' and 26 respectively until the bightthereof once more drops below he upper switches LUV and RUV.

From the foregoing it will be seen that the operation of the tape reels16 and 1S is in effect a self-compensating operation whereby the tapeloops in the control columns 2@ and 26 are maintained in an optimumposition. Furthermore, it is apparent that the controls for the reels iand 12% are independent one from thc other.

The second contact point of each vacuum switch is used to provide acircuit for their respective brake coils. When the control circuit isdescribed, it will appear that a circuit is established through closedpoints of switches LUV and LLV to energize the coil of the lile reelbrake 42 and that a circuit is provided through closed points ofswitches RUV and RLV to energize the coil in the machine reel brake e8.It is intended that the brake coils be energized whenever the reelingand unrceling clutches are deenergized.

The mechanism for driving the tape through the tape head 16 in a forwarddirection is shown in FIG. l0 of the drawings, FIGS. ll through 13diagrammatically illus trating the other drive and stop positions. Thedrive capstans 2S and 3i) are constantly driven by means of a motor 142(FIG. 3) whose shaft 144 rotates in a clockwise direction. The drivecapstans 23 and 3i) are journallcd for rotation in the face panel 13 ofthe machine, and the shafts 25a and 38a extend to the rear of the panel13 where they have atiixed thereto belt pulleys 145 and 148respectively. A drive belt 159 is trained about the pulleys 146, 143 andabout a motor shaft pulley 152 so that upon clockwise rotation of themotor shaft 1:14 the capstan shaft ZSa will be rotated in a clockwisedirection while the capstan shaft 30a will be rotated in acounterclockwise direction. This is accomplished by the use of an idlerpulley 154 mounted on a spring-biased lever 156.

Ey reference to FIG. 10 of the drawings it will be seen that the tapemoving idler pulleys 32 and 34 are mounted for rotation at the free endof levers 158 and 166 respectively. The inner ends of the levers 15S andit) are lixed to pivot shafts 162 and 161.1 respectively. The pivotshafts 162 and 164 are journalled for rocking move` ment in the facepanel 13, and each of these shafts has attached thereto a short,upwardly extending link 166 and 168 respectively. The inner, free endsof the links 166 and 168 have pivoted thereto levers 170 and 172respectively which have their opposite ends pivoted to a commonoperating lever 174.

With the foregoing structure the tape moving idler pulleys 32 and 34 maybe selectively engaged with their related drive capstan and with theirstop capstan. Thus the tape moving idler pulley 32 may be brought intocontact with the reverse drive capstan 28 or with the forward stopcapstan 36. 'Ihe tape moving idler pulley 34 may be selectively engagedwith the forward drive capstan 30 `or with the reverse stop capstan 38.The stop capstans 36 and 38 are eccentrically mounted in the face panel13 ,by means of screws 36a and 38a about which the capstans may beadjusted to vary their braking effect.

In order to impart controlled movement to the tape moving idler pulleys32 and 34, there has been provided herein a forward-reverse actuator 176comprising a pair of aligned, high speed relay magnets 176e and 176b anda stop or drive actuator 178 which consists of a coil 180 in a field ofhigh flux density caused by a permanent magnet 182. The high speed relaycoils 176e and 176b are mounted on a supporting yoke in axial relationto each other and with the provision of a space between the magnets toaccommodate a pivoted armature 184 to the free end of which theoperating lever 174 is attached by means of a pivot stud 186.

The coil 180 of the stop-drive actuator has affixed thereto a rod 188which is connected to the operating lever 174 midway between theconnections of the levers 170 and 172.

When the relay magnet 17612 is energized, the armature 184 will beattracted thereto and the operating lever 174 will be biased to theright in FIG. 10. VThis elevates the tape moving idler 32 a half gapwidth above the tape moving idler 34. When the stop-drive actuator 178is energized to repel the coil 180 thereof, an upward thrust will .bedelivered to the rod 188. This will further move the drive linkage toforce the tape moving idler pulleys downwardly and outwardly until thetape moving idler pulley 34 is engaged with the forward drive capstan38. This will cause the tape 14 to be driven downwardly into the controlcolumn 26.

The foregoing describes one of four stable positions into which the tapemoving idler pulleys may be biased. The three other positions areillustrated in FIGS. 11, 12 and 13 of the drawings.

FIG. 1l shows the position of the tape moving idler pulleys for stoppingtape feed following forward feed of the tape. At this point it may beappropriate to mention that the tape is always pulled through the tapehead 16 and is stopped by braking the tape at a position behind the tapehead 16. This will insure sufficient tape tension at the tape head 16 atall times.

Reverting to FIG. 11 of `the drawings it will be seen that the tape 14is stopped by engaging the tape between the forward stop capstan 36 andthe tape moving idler pulley 32. To achieve this function, the magnet176b must remain energized, but the flow of current through thestop-drive actuator 178 is reversed whereby the coil 180 is attracted tothe permanent magnet 182. 'Ihis results in a downward pull on the rod188. Such pull on the linkage system will tend to raise both tape movingidler pulleys 32 and 34, but since the tape moving idler pulley 32 inthe forward drive position was higher than the pulley 34, the idlerpulley 32 engages the forward stop capstan 36 to brake tape movement.Engagement between the tape moving idler pulley 32 and its forward stopcapstan 36 results from the upward bias given to the tape moving idlerpulley 32 under the influence of the magnet 176b.

In FIG. 12 of the drawings, the tape 14 is moving in a reversedirection. To bias the tape moving idler pulley 32 into contact with thereverse drive capstan 28, it is necessary to energize the magnet 176:1.This attracts the armature 184 and pulls the operating lever 176 to theleft in FIG. 12. This will serve to drop the tape moving idler pulley 32one-half gap below the idler pulley 34 and condition the tape movingidler pulley 32 for engagement with the reverse drive capstan 28 whenthe moving coil 180 is energized to cause an upward'movement of the rod188. Such movement will serve to project the tape moving idler pulley 32into engagement with the reverse drive capstan 28, whereby the tape 1410 is driven in a reverse direction, i.e. from right to left in FIG. 3of the drawings.

The reverse stop position of the tape drive mechanism is shown in FIG.13 of the drawings, wherein the tape moving idler pulley 34 is broughtinto engagement with the reverse stop capstan 38. To achieve thisengagement, the magnet 17651 must remain energized but the current inthe moving coil is reversed, whereby the coil is pulled downwardly sothat the rod 188 exerts a downward pull on the operating lever 174 witha consequent upward bias of the tape moving idler pulley 34 into contactwith the reverse stop capstan 38.

In FIG. 1 is shown a pair of tape contact arms 190 and 192. These armsare mounted for pivoting movement so that the ends thereof may ridefreely in Contact with the tape coils on the respective reels 10 and 18.Through this medium is provided a control mechanism to prevent thecomplete run-out of tape from the reels. FIGS. 14 through 20 illustratethe particular details of one form of tape arrn mechanism, while FIGS.2l through 23 show a modified form. Specific reference may rst be madeto that form of the mechanism shown in FIGS. 14 through 120.

The tape arms 190 and 192 have tape contacting rollers 194 and 196 atthe free ends thereof. These rollers are freely rotatable in thebifurcated free end of the arms 190 and 192 respectively, so that theyride lightly on the tape coil of the tape reels 10 and 18. The innerends of the arms 190 and 192 are keyed to shafts 198 and 21H)respectively. These shafts are journalled for rocking movement in amounting block 202 which has a flange 204 by means of ywhich themounting block is mounted in the face panel 13 of the machine as shownin FIGS. 1 and 18. An operating shaft 206 is mounted for rockingmovement in the block 202 at a point midway between the shafts 198 and200 .and slightly thereabove. The forwardly projecting end of theoperating shaft 206 has an operating handle 208 affixed thereto.

The distal ends of the shafts 198, 200 and 206 extend beyond the rearface of the mounting block 202 at which point intermeshing gears aremounted on the respective shafts. The shafts 198 and 200 have mountedthereon a pair of gears for limited rotation in respect to the shaft.FIG. 17 of the drawings illustrates one of these gears which may berecognized as the gear 210 on the shaft 200. The other shaft 198 has agear 212 mounted thereon in similar fashion to permit limited relativemovement between the shaft and the gear.

The relative movement between the shafts 198 and 200 and theirrespective gears 212 and 210 is for the purpose of permitting movementof the respective arms 190 and 192 and a pair of contact making andbreaking fingers 228 and 222 which are fixed to the ends of shafts 198and 2110, respectively, without reference to rotation of the operatinghandle 208.

With reference to FIGS. 17, 19 and 20 of the drawings, it will be seenthat the gears 210 and 212 `are formed vwith a pair of outwardlydiverging slots, and that a pair of pins 214 and 216 carried by theshafts 200 and 198, respectively, extend into the slots of theirassociated gears. Thus while the gears 210 and 212 are adapted forlimited movement in respect to their respective shafts 200 and 198, theslot walls will engage the pins 214 and 216 and rotate the shafts 198and 200 when engagement between the pins and the slot walls is effected,as during rotation of the handle 208.

The manner in which movement of the handle 208 is imparted to the gears210 and 212 is as follows. The operating shaft 206 has a gear 218 keyedthereto, and this gear, as best seen in FIG. 16 of the drawings, is indrlving contact with the gear 212, this latter gear being relativelywide. The gear 210 in turn is in mesh with and drives the gear 212. Bymeans of this arrangement, rotation of the shaft 206 is imparted throughthe gear 218 to the gear 212 and to the gear 210 with the consequencethat the shafts 198 ,and 200 are rotated when the 11 respective pins 216and 214 come into engagement with the slot walls in their associatedgears.

As intimated hereinabove, the shafts 198 and 200 have attached thereto apair of circuit making and breaking fingers 228 and 222, respectively.The free ends of these fingers mount adjustable studs 224 and 226,respectively. Contact between the studs 224 and 226 and a pair ofnormally open tile and machine reel contacts FRS and MRS, respectively,shown at the top of FIG. 3 of the drawings will influence the controlcircuit as will be more fully described at a later point herein.

From the foregoing it will be seen that rotation of the handle 208 willtransmit a torque through the gears to the tape contact arms 19t) and192 and to the circuit making .and breaking fingers 220 and 222 toelevate the arms and the fingers. While the lost-motion connectionbetween the gears 210 and 212 and their respective shafts 281) and 198permits raising of the tape contact arms 198 and 192 and the circuitmaking and breaking fingers 228 and 222, the contact arms 190 and 192,and consequently the circuit making and breaking fingers 220 and 222,are free to follow the tape coil on the reels 18 and 18.

The inner end of the operating shaft 206 has a plate 228 attachedthereto, and this plate carries .a pair of rearwardly extending studs230 and 232. The stud 230 supports one end of a coil spring 234 whichhas its other end attached to a fixed pin 236. The stud 238 is solocated on the plate 228 that the torque of the spring 234 is along aline which includes the shaft 296 when the operating handle 288 is in avertical or open position. Through this medium the mechanism justdescribed has a stable, open position under the influence of the spring234. The second stud 232 mounts an operating link 238 by means of whicha tape head cover is opened and closed.

The tape head 16 (see particularly FIG. 18 of the drawings) has a cover240 pivoted on a block 242 which is attached to lthe rear face of themachine panel 13. Immediately to the rear of the tape head 16 andslightly thereabove is an aperture 244 through the face panel of themachine, providing passage for a rearwardly projecting extension 246 ofthe reading head cover 248. By reference to FIG. 18 of 4the drawings itwill be seen that the cover 240 is pivoted on the block 242 by means ofa pivot pin 248 about which the cover may rock into open and closedposition in respect to the head 16. A spring 250 is coiled :about thepivot pin 248 and has oppositely disposed portions, one of -whichengages the rear face of the machine face panel and the other of whichengages Ithe lower face of the rearwardly projecting cover extension246. By this arrangement the cover 240 is normally biased into closedposition.

Rocking movement of the shaft 286 in the bearing block 202 is limited bymeans of a stop plate 252 which is adapted to engage a stop pin 252:1 atythe rear of the face of the block 202. The stud 230 is also adapted toopen and close a thread handle switch THC as will be developed morefully hereinafter.

From the foregoing it will 'be apparent that whenever the operatinghandle 208 is rotated to a vertical position such as that shown in FIGS.and 18 of the drawings, the tape contacting arms 190 and 192, andconsequently the tape contacting rollers 194 and 196, will be raised sothat tape reels may be removed lfrom or placed upon the spindles 12 and20. At the same time, the circuit making and breaking llingers 220 and222 will be elevated. Concurrent with these movements is the opening ofthe tape head cover 240 -through stud 232, operating link 238 and therearwardly projecting cover extension 246. With the mechanism in open orelevated position, the spring 234 will hold the parts in such positionto permit the changing of reels and threading of tape as may berequired.

When the operating handle 208 is returned to its horizontal position,the tape sensing arms 190 and 192 will return to their normal positionin contact with the tape coil on the associated tape reels 10 and 18. Itmay be noted, however, that the lost-motion connection between theshafts 198 and 200 will permit independent movement of the tape sensingarms and 192 and ytheir associated circuit making and breaking fingersas may be required by the size of the tape coil on either of the reels10 or 18.

The modified tape contact arm mechanisms shown in FIGS. 2l Ithrough 23of the drawings have effective operations which are substantially thesame as those of the form shown in FIGS. 14 through 19 of the drawingsbut perform these operations in a somewhat different fashion. In thisform of `the invention a pair of tape contact arms 254 and 256 are`secured to the front end of a pair of shafts 258 and 260, respectively.The shafts 258 and 260 are mounted for rocking movement in a mountingblock 262 which has a flange 264 by which the block may be mounted inthe `face panel 13 of the machine. Attached to the rear end of ltheshafts 258 and 260 are a pair of circuit making and breaking fingers 266and 268, respectively. Mounted for free rotation on the shafts 258 .and260 are a pair of gears 270 and 272 respectively. These gears haveelongated hubs 274 like lthat shown in reference to the gear 272 in FIG.22 of the drawings. Afiixed to the elongated hub portion of the gearsfor rotation therewith are a pair of fingers 276 Iand 278. Each of Ithecircuit making and breaking fingers 266 and 268 has an outwardly turnedflange portion 280 and 282, respectively, which overlies the outerextremities of the ngers 276 and 278, respectively. As a consequence ofthis relationship, whenever the fingers 276 and 278 are elevated, theirextremities may engage their related flanges 288 and 282 respectivelyand thereby elevate the circuit making and breaking fingers 266 and 268.This motion results in the rocking of shafts 258 and 260 with the resultthat the tape contact arms 254 and 256 are also elevated. The circuitmaking and breaking fingers 266 and 268 have at their extremitiesadjustable studs 284 and 286, respectively, which are adapted to contactand close the reel switches FRS and MRS, respectively, `shown in FIG. 3of the drawings when either or both of these circuit making and breakingfingers are in their lower position. Thereby, the reel switches will beclosed whenever the coil of tape on either reel becomes dangerouslydepleted.

In order to manually raise and lower the tape sensing arms 254 and 256and their related circuit making and breaking fingers 266 and 268, anoperating shaft 288 is journalled `for rocking motion in the block 262.An operating handle 290 is fixed to the forward end of the shaft 288.The rear end of the shaft 288 has attached thereto a cam plate 292 towhich is pivoted one end of a link 294. The other end of the link 294 ispivoted to the finger 278 so Ithat rocking movement of the shaft 288will be imparted to the finger 278 and thereby to the gear 272. Thegears 270 and 272 being in mesh with each other will transmit operatingtorque from the gear 272 to the gear 271) and thereby to the otherfinger 276.

It will be seen from the foregoing description, with particularreference to FIG. 23 of the drawings, that a mechanism has been providedwherein manual rotation of the handle 290 will cause rotation of thegears 278 and 272 with .the consequent rocking movement of the fingers276 and 278. When the handle 290 is rocked to `a vertical position, andif the tape sensing arms 254, 256 and the circuit making and breakingfingers 266 and 268, or either of them, are in a lower position, suchmovement of the handle will be effective to rotate the shafts 258 and260 and thereby elevate the `tape sensing arms 254- 256 and -the circuitmaking and breaking fingers 266 and 268.

In lieu of the springs 234 used in the previously described form of themechanism for imparting stability to the assembly in its open position,there has :been provided in the modified form a springpressed detent 29613 which is `adapted to engage a recess 298 in -a hub 300 fixed to .theshaft 288.

In this modified form of the mechanism the cam plate 292 operates bothIas an effective stop and .as an oper-ator -for the thread handle switchTHC. The thread handle switch THC (FIG. 2l) is so positioned that theedge of the cam plate 292 that is adjacent its junction with the link294 comes into contact with the thread handle switch to c-lose the same.The `cam plate 292 has a `shoulder portion 302 which limits the rockingmovement of the shaft 288 in one direction by engagement with a `stoppin 304 which projects from the rear face of the mounting block 262.Rocking movement of the shaft 288 in the opposite direction is limitedby engagement between the upper edge of lthe cam plate 292 and the hubportion of the finger 278.

lt will be observed that the modified form of the tape sensing mechanismembodies no mechanical connection for the tape head cover. This is dueto the fact that it is contemplated to use the moditied form of the tapesensing assembly with a tape head which is bodily slidable in a verticalpath in the face plate of the machine, and which is under the control ofa solenoid which may be impulsed in any suitable fashion whenever it isdesirable to drop the tape reading head from its normal tape readingposition.

FIGS. 24, 25 and 26 of the drawings illustrate the structure of amodified form of tape head 16a. Herein the tape head lhas a cover 240gsupported on a plate 306 which projects forwardly from the face panel 13of the machine. It is contemplated in this structure that the tape head16a be dropped away from its cover 240a rather than separation of thecover from the reading head as in that form shown in FIG. 18 of thedrawings.

To secure this function, the tape head 16a is secured to a base plate308 which is mounted for sliding movement on the face panel 13 of themachine between a pair of guides 310 and 312, the base plate 308 beingmounted in the guides 310 and 312 by means of anti-friction bearings314.

The base plate 308 and consequently the tape head 16a is held in itsupper or operative position by means of a pair of coil springs 316. Itmay be noted that extending rearwardly from the base plate 308 andthrough a pair of slots 318 in the face panel of the machine are a pairof studs 320 to which one end of the coil springs 316 are attached, theother ends of the coil springs 316 being fixed to studs 322 projectingrearwardly Ifrom the face panel of the machine. It will be seen,therefore, that while the base plate 308 is adapted for movement in avertical path within the guides 310 and 312, the same is normally heldin its upper position where it is in juxtaposition to the cover 240aunder the influence of the coil springs 316.

Whenever it becomes necessary to drop the tape head 16a away from itscover 240a, as may be the case when tapes are changed, there has beenprovided in this form of the mechanism an operating solenoid 324comprising a coil 326 and a core 328. The outer end of the core 328 haspivoted thereto a link 330 which at its other end is pivoted to arocking lever 332. The rocking lever is mounted midway between its endson a pivot stud 334 so that whenever the coil 32S of the solenoid isenergized yand its core is pulled into the coil, the upper end of therocking lever 332 will swing in an arc. This motion is utilized to pulldown the base plate 308 against the tension of the springs 316 by aconnection between the upper end of the rocking lever 332 and a link 336which is pivoted to a stub shaft 338 fixed to the base plate 308 andextending rearwardly therefrom through a slot 340 in the face panel ofthe machine.

It follows from what has been said in connection with the structureshown in FIGS. 24 through 26 that whenever the coil 326 of the solenoidis energized, its core 328 will be attracted and the linkage systemcomprising link 330, rocking lever 332, `and link 336 will operate topull the base plate 308 and its associated tape head 16a downwardly andthe same will be held in such posi- .tion so long as the solenoid 324remains energized. Upon deenergization of the solenoid 324, the coilsprings 316 with the aid of a spring 317 will return the base plate 308and its associated tape head 16a to its upper or operative position.

The mechanism is put into operation by closure of the line switch LS(FIG. 30) which supplies 115 Volt alternating current to the vacuum pumpmotor VPM. The same circuit includes transformers T (onlydiagrammatically indicated) from which are derived the 40 volt powersupply and the high voltage power supply. Most of the relays, such asthose shown in FIG. 29, are connected across the 40 volt power supplyline, while the high voltage supply provides the various plate voltages,bias voltages, etc. required by the several electronic units.

As soon as Voltage appears on the +40 volt line, the run relay R1 (FIG.29) is energized through the thread handle contact THC and the safetyvacuum switch contact SVS. If there is a tape loop in the controlcolumns 24 and 26, thus forming an air seal between the upper and lowervacuum switches, and if the vacuum motor VPM is operating, the safetyvacuum switch SVS in the header 108 (FIG. l) will be closed by thevacuum built up in the header 108 by the vacuum pump. If the tapesensing arm operating handles 208 or 290 are in a horizontal position,the thread handle contact THC will be closed.

When the relay R1 is energized, its associated point Rl-l closes,thereby energizing a heavy duty relay HD'. Energization of the heavyduty relay HD causes its HD1 point (FIG. 30) to close and its HD-2 andHD-3 points (FIG. 29) to transfer.

By reference to FIG. 30 of the drawings, it will be seen that closure ofthe HD-l point closes the circuit of the capstan motor 142 as well asthe circuit of the two reel motors 22 and 23.

If it is desired to feed tape from the file reel 10' to the machine reel18, a forward key FK (FIG. 28) is pressed to open its contact, or ifreverse feed from the machine reel 18 to the file reel 10 is required, abackward key BK is depressed to open its contact. Depression of theforward key FK, for example, removes the -1250 volt bias supply from theright side of a binary trigger. As a result, the right side of thetrigger is rendered conductive, while the left side is renderednon-conductive. With the left side of the trigger being non-conductive,its plate voltage is high. Thus the voltage on the tube side of acathode resistor of an associated cathode follower CF1 is high and thegrid of a connected power tube PTS is high. With the grid of the powertube PTS being high, the power tube PTS conducts heavily and the forwardcontrol magnet 176b is energized. This will condition the tape movingidler pulley 34 for driving engagement with the forward drive capstan30.

Thereafter actual tape feeding in -a forward direction is started bydepressing -a tape feed control switch TFS (FIG, 27). Transferring ofthis switch applies 30 volts to the grids of ya power tube PT1 and apower inverter P11, while -l-lO volts are applied to a power tube PT2and a power inverter P12. Power tube PT2 and power inverter P12 are thusrendered conductive, While the power tube PT1 and power inverter PII arerendered non-conductive. When the power tube PT2 conducts, it energizesthe relay B. However, it takes an appreciable time for the relay B tobecomek sufficiently energized to open its RB point. During thisinterval by which relay point RB opens, the Afollowing action takesplace. As the power nverter P11 goes non-conductive, its plate swingspositive. This positive swing is applied to the grid of a thyratronTI-Ifl and the grid of a power tube PT4. The thyratron THl fires and thepower tube PT4 is rendered conductive. The firing of the thyratron THlin effect shorts out re-

